OpenLara on FireTV Cube: just a white head

First, let me tell you that I have two FireTV devices: one is a FireTV Stick 4K, the other is a FireTV Cube – and yes, the FireOS versions are different: 6.2.9 vs. 7.2.8. The RetroArch version is the same on the Stick and the Cube, as is the OpenLara core and the PC game data. On the Stick it works, albeit a little slowly and for the first screens (until the house) I can’t see anything; but luckily the menus work. On the Cube, once I am in the house, everything is black except for the head of Lara, which is all white. I can move and stuff, hear the sounds, but it’s all black. Does anyone have this issue? Even better: a solution?